How accurate are low-dose CT scans for lung cancer?


Lung cancer is the leading cause of cancer-related death in the United States. Screening with low-dose computed tomography (called low-dose computed tomography or LDCT) can save lives for people at high risk of getting this disease.

Although effective in detecting lung cancer, LDCT screening carries some risks.

In this article, we discuss the benefits, risks, and accuracy of low-dose CT scans for detecting lung cancer. We also look at who should be screened for lung cancer and how often screening should take place.

Low-dose CT scans are the only screening test recommended by the Centers for Disease Control and Prevention (CDC) for the early detection of lung cancer. This test uses x-rays to create cross-sectional images of the lungs and lymph nodes in the chest. It also uses low doses of radiation to locate tumors in the lungs.

The many detailed images generated by an LDCT can identify nodules or masses in the lungs before symptoms appear. The earlier lung cancer is detected, the better your chances of successful treatment.

As with any screening test, low-dose CT is not perfect. It cannot distinguish malignant tumors from benign (non-malignant) tumors and may not detect all tumors. Benign tumors that are discovered will require additional testing which can be invasive.

About False Positive Test Results

False positive results also occur. A Analysis and study 2021 provide up-to-date information on low-dose CT screening to the US Task Force on Preventive Services found that LDCT screening reduced lung cancer deaths. He also found that the incidence of false positives was significant.

For this analysis, the researchers looked at several studies. They found false positive rates ranging from 9.6% to 28.9% for initial baseline testing. False positives can lead to emotional distress. They can also lead to unnecessary and invasive surgical tests, which carry additional risk factors.

About Overdiagnosis

Another risk of LDCT screening is overdiagnosis of lung cancer. Overdiagnosis occurs when tumors are discovered that will never cause a health problem. This may be because the tumors are indolent (slow growing). It can also be due to a person’s advanced age or reduced life expectancy for other reasons.

As with false positive results, overdiagnosis can lead to unnecessary testing and emotional turmoil.

Chest X-rays are quick and inexpensive. If your doctor suspects you have a condition involving your chest, a chest x-ray will usually be the first test ordered.

Advantages and disadvantages of chest X-rays

But chest X-rays are not recommended as screening tools. Unlike CT scans, chest X-rays are not useful for detecting small tumors early. They also cannot be used to distinguish between cancerous tumors and other lung conditions, such as a benign lung abscess.

A Retrospective observational study 2021 found that the false negative rate of chest X-rays for lung cancer was 17.7%.

An older multicenter study published by the National Institutes of Health (NIH) found that annual chest x-rays do not reduce lung cancer death rates.

Advantages and disadvantages of CT scans

CT scans also use X-rays, but the technology differs from that used for a standard chest X-ray. Unlike a chest X-ray which generates one or two images, CT scanners take tens or even hundreds of images. A computer then combines these images to show a very detailed picture of your lungs.

CT scans identify more early tumors than chest X-rays. They are useful for assessing the size, position and shape of the tumor. CT scans can also identify some cases of cancer spreading to lymph nodes in the chest.

Lung cancer screening tests may be done annually for eligible high-risk individuals.

Diagnostic tests, such as a biopsy, will be done if lung cancer is found or suspected after a CT scan. Unlike screening tests, diagnostic tests for lung cancer are only done when cancer is suspected.

Other imaging tests may be requested if cancer is strongly suspected or proven by biopsy, as described in the table below.

The American Task Force on Preventive Services recommends annual low-dose computed tomography (LDCT) screening for people who meet these three criteria:

  • Have a 20 pack-year history of smoking cigarettes. (A pack-year is defined as having smoked, on average, one pack of cigarettes per day for 1 year. A 20-pack year can be defined as having smoked 1 pack per day for 20 years or 2 packs per day for 10 or more years)
  • Currently smoke or have quit smoking within the past 15 years
  • You are between 50 and 80 years old

By USPSTF and CDC Guidelineslung cancer screening should be discontinued once a person has not smoked for 15 years or develops a health condition that severely limits life expectancy or the ability or willingness to undergo curative lung surgery.

People with a history of heavy smoking are at risk for lung cancer. Lung cancer is the leading cause of cancer death in the United States.

Annual screening for lung cancer with a low-dose CT scan (LDCT) is recommended for those at high risk. Your smoking history and age are determining factors for the test.

Low-dose CT scans are the only screening test currently recommended for annual lung cancer screenings. Early detection of lung cancer has been shown to save lives. However, this test is not without risk.

Talk to a doctor about the benefits and risks of annual screening for you.


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